Quite often there is a need for application of a label on a surface that already has a pre-existing permanent printing on it, for example a silk screen printing, which cannot be removed without destructive treatment of the surface. This need may arise in the case of a container, such as a plastic crate for (beer) bottles or other goods, that is used for different brands or promotional items.
It has already been proposed and applied in practice to glue an opaque paper or plastic label on top of the pre-existing printed images.
Recently, much attention has been directed to the application of labels by image transfer to a surface. Image transfer is defined as the process of transferring a reverse printed ink-only image from a backing material (carrier web) onto a receiving surface, such as that of a bottle or a crate.
There is a need for using this system of image transfer in relation to applying labels over pre-existing permanent printed images. However, this has the problem that the conventional ink-only labels (image transfer) generally do not provide sufficient opacity to fully cover and mask the pre-existing print and the color of the article on which the label is to be applied. Inclusion of a conventional white layer in the transfer label based on titanium dioxide, zinc oxide and/or calciumcarbonate pigments can create problems with the printing of the label onto the backing layer and with the transferability of the label material to the substrate surface. Generally more than two layers of white pigmented ink have to be used, to provide sufficient opacity to mask the pre-existing print and/or the color of the substrate article.
There is a need for preventing possible bleed through from affecting the new label image. Bleed through of the background color could affect tone, hue and/or brightness of the image. There is a need to prevent this.
There is accordingly a need for an improved label material wherein at least one opaque layer is present, which serves, among others to hide an existing imprint, while at the same time providing at least equivalent processing characteristics in terms of label printing and transfer.
The invention is directed to a transfer label material for image transfer, comprising a backing material and a transfer layer, said transfer layer at least comprising an image layer, an adhesive layer and a pigmented layer between the adhesive layer and the image layer, said pigmented layer comprising a binder material, a pigment and at least 0.1 wt. %, calculated on the basis of the dry weight of the pigmented layer, of aluminium powder.
It has been found that adding a relatively small amount of aluminium powder to at least one pigmented layer results in an opacity, sufficient to hide an existing underlying printing and/or to prevent bleed through of the background color. The amount of aluminium powder can be kept quite low, up to 5 wt. %, preferably between 0.1 and 1.5 wt. %.
The aluminium powder may be used as such, or incorporated in a suitable matrix material such as a fat derivative, incluidng but not limited to fats and oils, fatty acids, fatty acid esters and the like.
In view of the printing properties of the pigmented layer it is preferred to use aluminium powder with a particle size of between 1 and 100 μm, preferably between 5 μm and 50 μm.